1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and a production method therefor.
2. Description of the Related Art
FIG. 9 shows an example of an equivalent circuit of an active matrix liquid crystal display apparatus configured by using thin-film transistors (hereinafter referred to as "TFT") as conventional switching devices, that is, an equivalent circuit referred to as "Cs on Common system." Pixel electrodes 106 are formed in a matrix shape. A TFT device 101 used as a switching device, is connected to each of the pixel electrodes 106. A gate line 102 used as a scanning line is connected to the gate electrode of the TFT device 101. The TFT device 101 is driven by a gate signal supplied to the gate electrode. In addition, a source line 103 used as a signal line is connected to the source electrode of the TFT device 101. When the TFT device 101 is driven, a data (display) signal is supplied to the pixel electrode 106. The gate lines 102 and the source lines 103 are provided around the pixel electrodes 106 arranged in a matrix shape so as to intersect with one another at right angles. Furthermore, the drain electrode of the TFT device 101 is connected to the pixel electrode 106 and an additional capacitance (Cs in FIG. 9). The electrode opposite to the additional capacitance is connected to a common line 104 (hereinafter referred to as "Cs line"). This configuration is used to drive liquid crystal (C1c in FIG. 9) disposed between an counter electrode 118 and the pixel electrode 106.
FIG. 10 is a plan view showing a pixel of an active matrix substrate of a conventional liquid crystal display apparatus. In FIG. 10, the gate lines 102 and the source lines 103 shown in FIG. 9 are formed on a transparent substrate so as to intersect with one another at right angles. Near each intersection, the TFT device 101 is formed as a switching element. A contact hole 107 provided in an inter-layer insulation layer (not shown) is connected to the pixel electrode 106 via a connection line 105. The connection line 105 is overlapped with the Cs line 104 via a gate insulation film (not shown) so as to form an additional capacitance. Moreover, the pixel electrode 106 partially overlaps with the gate line 102 and the source line 103 via the inter-layer insulation layer.
FIGS. 11A and 11B are sectional views of the liquid crystal display apparatus shown in FIG. 10. Referring to FIGS. 11A and 11B, the gate line 102 shown in FIG. 10 and a gate electrode 112 are formed from tantalum, aluminum or the like on a transparent substrate 110, such as a glass substrate, in the first place. A Cs line 104 is formed together with the gate line 102 and the gate electrode 112, a gate insulation film 111 is formed from silicon nitride, silicon oxide or the like, a semiconductor layer 114 is formed from amorphous silicon, polysilicon or the like, and an n+ silicon layers for forming a source electrode 113 and a drain electrode 115 is formed in this sequence.
Next, a transparent conductive film and a metallic film formed from tantalum, aluminum or the like for forming a source line 103 and a connection line 105 are formed in this sequence by the sputtering method so as to perform patterning in predetermined shapes. Over the formed films, an photosensitive acrylic resin having a dielectric constant of 3.4 is formed as an inter-layer insulation film 108, for example, at a film thickness of 3 .mu.m by the spin coating method. This resin is exposed to light in accordance with a desired pattern and subjected to development by using an alkaline solution. As a result, only the exposed portions are etched by the alkaline solution, whereby contact holes 107 passing through the inter-layer insulation film 108 are formed.
Furthermore, on top of the film, a transparent conductive film, for forming a pixel electrode 106 is formed by the sputtering method and is subjected to patterning. As a result, the pixel electrode 106 is connected to the connection line 105, which is connected to the drain electrode 115 of the TFT device 101, via the contact hole 107 passing through the inter-layer insulation film 108. This completes the production of an active matrix substrate.
On the other hand, three-color (red, green and blue) filters 120a, 120b (only two color filters are shown in FIGS. 11A and 11B) and counter electrodes 118 are formed on a transparent substrate 117, such as a glass substrate. Liquid crystal 125 is disposed between such an opposing substrate and the above-mentioned active matrix substrate, and bonded together by using a sealing agent (not shown). In order to prevent light leakage from the TFT device, a light shielding film 140 is provided on the opposing substrate disposed above the TFT device 101. Furthermore, an alignment film (not shown) and a polarizing plate (not shown) are used as necessary.
With this structure, the aperture ratio of the liquid crystal display apparatus can be raised, and electric fields caused by the lines 102, 103 are shielded, thereby making it possible to suppress disclination.
FIG. 12 is a magnified plan view of a TFT device on the active matrix substrate shown in FIGS. 10 and 11A. Referring to FIG. 12, the semiconductor layer 114 is provided on the gate electrode 112 branched from the gate line 102 via a gate insulation film (not shown). On top of the layer, an n+ silicon layer for forming the source electrode 113 and the drain electrode 115 is provided via a predetermined gap. The source line 103 used as a data signal line is connected to the source electrode 113 at a portion branched from the source line 103. In addition, the connection line 105 (not shown) is connected to the drain electrode 115.
Generally, in order to accomplish color display in the liquid crystal display apparatus, color filters are formed on the opposing substrate, and in order to prevent color mixture and light leakage, a light shielding film being referred to as "black matrix" is formed bet ween the pixel electrodes 106 and at a portion opposite to the TFT device 101. However, a structure without a black matrix on the opposing substrate has been contrived in order to lower product ion cost.
In this case, light shielding between pixel electrodes 106 can be attained at the lines 102, 103, but not at the upper portion of the TFT device. In the case of a switching device such as a TFT device comprising a semiconductor layer, carriers are generated when the semiconductor layer is exposed to light, and off-current increases, causing crosstalk, improper contrast and uneven display, and significantly deteriorating display quality. This is caused by the reason described below. That is, in case the inter-layer insulation film 108 is provided on a TFT device, in particular, in case a thick resin film is formed, display is apt to be affected by stray light.
An active matrix liquid crystal display apparatus in accordance with another prior art has also been disclosed in Japanese Unexamined Patent Publication JP-A 6-130416 (1994), for example. This publication discloses a structure wherein a light shielding film is formed on the side of an active matrix substrate or an opposing substrate.
FIG. 13 is a sectional view showing an active matrix type liquid crystal display apparatus 217 disclosed in Japanese Unexamined Patent Publication JP-A 6-130416 (1994). In the liquid crystal display apparatus 217, a light shielding film is provided on the side of the active matrix substrate. In the liquid crystal display apparatus 217, a liquid crystal layer 216 is disposed between an active matrix substrate 214 and an opposing substrate 215.
The active matrix substrate 214 is formed as described below. Gate lines, which have a plurality of gate electrodes 201 on one of the surfaces of the transparent substrate 200 on the side of the liquid crystal layer 216, are formed in parallel with one another. A plurality of source lines are formed in parallel with one another in the direction orthogonal to the gate lines. Pixel electrodes 209 and TFT devices 218 are formed at a plurality of regions surrounded by the gate lines and the source lines intersecting with one another.
In the TFT device 218, the gate electrode 201 is covered with the gate insulation film 202, a non-dope a-Si layer 203 is provided on the gate insulation film 202, and N+ type a-Si layers 204, 205 are provided on the a-Si layer 203. A source electrode 206, to which the source line is connected, is provided on one of the N+ type a-Si layers, that is, 204. Furthermore, a drain electrode 207, to which the pixel electrode 209 is connected, is provided on the other N+ type a-Si layer, that is, 205. The TFT device 218 is connected to the pixel electrode 209 via the drain electrode 207. However, an inter-layer insulation film 208 is disposed at portions other than the drain electrode 207. Moreover, a Light shielding film 210 is provided on the TFT device 218 via the inter-layer insulation film 208.
The opposing substrate 215 is formed as described below. An counter electrode 212 opposite to the pixel electrode 209 is formed on one of the surfaces of the transparent substrate 211 on the side of the liquid crystal layer 216, and an alignment film 213 is formed to cover the counter electrode 212.
In this kind of structure having the light shielding film 210 via the inter-layer insulation film 208, when light enters from the side of the opposing substrate 215, it is possible to prevent light from entering the a-Si layers 203, 204 and 205 of the TFT device 218. However, when light enters from the side of the active matrix substrate 214, carriers are generated by the light reflected by the light shielding film 210, and display quality is deteriorated.